Reconnecting tile drainage to riparian buffer hydrology for enhanced nitrate removal

Area of Science:

• Agricultural Science
• Environmental Science
• Water Quality Management

Background:

• Riparian buffers effectively remove nitrogen (N) from surface and groundwater.
• Artificial subsurface (tile) drainage in agricultural fields bypasses buffers, limiting N removal.
• Existing tile drainage systems hinder the natural N-filtering capacity of riparian buffers.

Purpose of the Study:

• To investigate the feasibility of re-routing tile drainage through riparian buffers to enhance nitrogen removal.
• To assess the impact of subsurface flow redirection on nitrogen dynamics within riparian buffers.
• To evaluate a novel management practice for improving water quality in tile-drained agricultural landscapes.

Main Methods:

• Intercepted a field tile outlet and redirected a fraction of its discharge as subsurface flow into an adjacent riparian buffer.
• Infiltrated tile drainage via a perforated pipe installed below the surface within a 60-m-wide buffer.
• Monitored water table levels and nitrogen concentrations in shallow groundwater over a 2-year period.

Main Results:

• Over 55% of the total tile flow was successfully redirected as subsurface infiltration within the riparian buffer.
• The redirected flow raised the water table within the buffer by approximately 35 cm.
• A significant decrease in nitrogen concentrations in shallow groundwater across the buffer indicated substantial N removal.

Conclusions:

• Redirecting tile drainage as subsurface flow through riparian buffers is a feasible and effective method for increasing nitrogen removal.
• This practice holds promise for improving surface water quality in agricultural regions with extensive tile drainage.
• Nitrogen removal within the buffer likely occurred through plant uptake, microbial immobilization, or denitrification.